Import of Proteins into Mitochondria
The biogenesis of mitochondria involves a close interaction between the nucleocytoplasmic and the mitochondrial genetic system. The majority of the mitochondrial proteins are synthesized on cytoplasmic ribosomes and transported into the organelle (1). The mechanism of this protein import has been under debate for many years (e.g., (2,3)). Recent experiments with yeast cells have shown that several cytoplasmic- ally made mitochondrial proteins are initially made as larger precursors, both in vitro as well as in pulse-labeled yeast spheroplasts (4,5). So far, larger precursors have been detected for the following cytoplasmically made mitochondrial proteins: the three largest subunits of the mitochondrial F1-ATPase (i.e., the α, β, and γ subunit, see (4)) and two subunits of the mitochondrial cytochrome bc1 complex (cytochrome c1 and subunit V; (5) and C. Côté, unpublished). Import of in vitro synthesized precursors into isolated mitochondria was demonstrated for the three largest F1-ATPase subunits; as an operational measure of import, we checked whether any of the polypeptides added to the mitochondria became resistant to externally added proteases (4).
KeywordsChrome Polypeptide Cyanide Methionine Cytosol
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